A number of methods have been employed to dispense medicines or medications. When it is not possible to develop a patient-friendly form of administration, such as an orally administered tablet, it is necessary to introduce the medicine or medication directly into the body tissue or into the vascular blood system. Hypodermic needles are commonly used to inject liquid solutions or suspensions of a pharmaceutical agent into a patient's subcutaneous tissues.
Despite wide usage, hypodermic syringes present notable shortcomings. The sharp hollow needles can cause injury to the patient as well as to the medical personnel administering the injection. The spent needles also are a potential source of infection or means for communication of disease, and consequently the used needles must be handled as hazardous medical waste. The injections are generally painful because of the needle's penetration of the patient's skin and the volume (e.g., 0.01 to 0.5 ml) of the injected fluid. Additionally, administration by injection can require good eyesight and dexterity. This can be a problem for many patients who self-administer their injections. Thus, the overall process of administering an injection using the hypodermic syringe technique can be relatively costly, time-consuming and complex.
Liquid jet injection systems have been developed as a needle-free alternative to the hypodermic syringe. By that approach, a jet of liquid is ejected from an orifice at a high velocity that is capable of penetrating through tissue so as to deposit the medication subcutaneously. In comparison to hypodermic syringes, a liquid jet injections system may be less painful and may have a lower skill requirement for the user. The persons being injected also exhibit less psychological aversion to a liquid jet injection system than those being injected by means of a hypodermic syringe.
However, drug delivery by a liquid jet can cause skin damage and bleeding. Additionally, a relatively large amount of energy is required to displace the liquid volume and form the high velocity jet, e.g. pressures on the order of several hundred atmospheres. Although theoretical energy requirements are about 6 joules of mechanical energy in a period of about 200 milliseconds, mechanical and other system losses result in an actual energy requirement that is significantly higher, e.g. about 10 to 20 joules. The means for generating this large energy pulse includes large springs, compressed gas and pyrotechnic actuators. From a size and performance standpoint compressed gas and pyrotechnics are advantageous, however, they face regulatory barriers common to such devices for example the safety limitations or regulations on shipping and handling.
In addition for the hypodermic syringe technique or liquid injection system, the shelf life of liquid solutions or suspensions to be injected is most often less than that for dried powdered forms of medications or medicines. Consequently, some sensitive medications must be stored as dry powder and then mixed with a sterile liquid immediately prior to use. The process of preparing the solutions or suspensions for injection requires specialized skill and training as well as being time consuming and costly. Additionally, in less developed regions special preparations are usually required to provide an adequate source of sterile fluid and/or maintain the liquid solutions or suspensions.
PCT Publication No. WO 94/24263 reports a certain needleless syringe using supersonic gas flow for delivery of dry particles including therapeutic agents. In this needless syringe, at least one membrane is ruptured by a highs pressure gas source to generate a supersonic gas flow. In a particular embodiment, the publication describes using a small 60-atmosphere reservoir of helium as the gas source. As described therein, the rupturing of the membrane and the supersonic gas flow causes the medication particles to be accelerated to a velocity of about 800 to 1000 meters per second. It is also reported that the particles so accelerated penetrate a patient's skin to thereby deliver the medication. That described system has a number of shortcomings. The described syringe requires a high-pressure gas reservoir and release mechanism, or a mechanical equivalent, to generate the pressures required to establish supersonic flow conditions. Also, supersonic flow is noisy, and measures must be taken to reduce sound output. Thus, the PCT Application describes (e.g., at page 14) a silencer to receive the shockwave reflected back from the patient's skin. Despite the silencer, the device is very loud as a result of the fast release of high-pressure gas. Still further, because the system described in the PCT Application uses a pressurized gas source, the system faces regulatory barriers as with liquid jet injection systems that employ compressed gas.
It thus would be desirable to have new methods and devices for administering therapeutic agents to a patient. It would be particularly desirable to have new methods and devices that could administer dry therapeutics through a patient's skin. Such devices and methods preferably would be simple in construction, be less costly per injection than prior art devices and methods, would not require highly skilled users to utilize the device, would prove to be less painful than an injection administered by means of a hypodermic syringe and would prove to be less noisy than prior art devices.